1. Technical Field
The present invention relates to a wafer transfer apparatus, and more particularly, to a robot arm cleaning device for cleaning a robot arm in a wafer transfer apparatus under a normal stand-by state when the robot arm does not adsorb or suction a wafer.
2. Description
In general, the tendency toward gradually increasing density and smaller sized semiconductor devices, and the tendency toward multi-layer wire structures in a semiconductor device, worsen the step coverage of the device. In order to improve the step coverage, several kinds of planarizing methods, such as an SOG (Spin on Glass), an Etch Back and a Reflow, etc., are being developed so as to be applied to a planarizing process of a wafer.
Such wafer planarizing processes include a mechanical polishing method and a chemical polishing method. In the mechanical polishing method, a characteristic of a polished layer is changed due to the mechanical polishing process, which can cause a defect on a semiconductor chip. In the chemical polishing method, although the changed-process layer is not formed thereon, a precisely flattened shape cannot be obtained very well. Therefore, a planarizing process is required to execute a polishing work by combining this mechanical polishing method with the chemical polishing method. Such a process is known as a chemical mechanical polishing (CMP) process.
For the CMP process, a wafer is installed on a polishing head by a vacuum or surface tension. During the process, the wafer is held between a polishing pad provided on a polishing table, and the polishing head applying a constant pressure to the wafer. The polishing pad rotates while simultaneously the polishing head rotates and oscillates.
The wafer surface and the polishing pad are in contact with each other by the weight of the polishing head and an applied pressurizing force. Slurry, used as a process fluid, moves into a small gap between the contacting faces of the polishing pad and the wafer. Polishing particles from the slurry and surface projections of the pad perform a mechanical removing operation. Meanwhile, a chemical component in the slurry also performs a chemical removing operation.
A CMP system includes a wafer storing unit having a cassette for accommodating wafers to be polished, a rinsing unit for rinsing and drying the polished wafers, and a wafer transfer apparatus for transferring the wafers between these process units.
The wafer transfer apparatus of such a CMP system is provided with a valve unit for controlling a vacuum On/Off operation, such a valve unit being illustrated in FIG. 1.
Referring to FIG. 1, the valve unit includes a solenoid valve 60 for supplying or cutting off air by an electric control, and an air valve 62 for maintaining or releasing a vacuum state by air supplied from the solenoid valve 60.
Under a normal stand-by state, when a robot arm 64 of the wafer transfer apparatus does not adsorb or suction the wafer, the solenoid valve 60 is closed and air is not supplied to the N/C (Normal Close) air valve 62. Therefore, a vacuum nozzle 66 of the robot arm 64 is not maintained in a vacuum state. When, at this time, the vacuum nozzle 66 is not maintained in a vacuum state, air flows in through the vacuum nozzle 66 to thus maintain an atmospheric pressure state.
However, when the wafer transfer apparatus transfers a wafer, the solenoid valve 60 is opened and air is supplied to the N/C (Normal Close) air valve 62. When air is supplied to the air valve 62, the air valve 62 is opened, and thereby the vacuum nozzle 66 of the robot arm 64 maintains a vacuum state to thus suction or adsorb the wafer.
Thus, the robot arm 64 in the wafer transfer apparatus adsorbs or suctions the wafer by using the vacuum nozzle 66 in a vacuum state. However, when not adsorbing the wafer, the vacuum nozzle 66 adopts an atmospheric state, not the vacuum state. Therefore, a problem occurs that an alien substance or fumes, etc. is deposited on or in the vacuum nozzle 66 and clogs up the vacuum nozzle 66.
Therefore, it is an object of the present invention to provide a wafer transfer apparatus having a robot arm cleaning device, and an associated method of cleaning the robot arm, in which a vacuum nozzle of the robot arm is prevented from being clogged up by alien substances or fumes etc. when in a normal stand-by state wherein a wafer is not being suctioned or adsorbed by the robot arm.
Another object of the present invention is to provide a wafer transfer apparatus having a robot arm cleaning device, and an associated method of cleaning the robot arm, in which a vacuum nozzle is prevented from being clogged up by injecting air into the vacuum nozzle of the robot arm when in a normal stand-by state wherein a wafer is not adsorbed or suctioned by the robot arm.
In one aspect of the invention, in a wafer transfer apparatus of a semiconductor fabricating apparatus, a robot arm cleaning device comprises a solenoid valve for supplying or intercepting air by an electrical control, a first air valve for performing a control to maintain or release a vacuum state by air supplied from the solenoid valve, a second air valve for supplying or cutting off N2 gas by air supplied from the solenoid valve, and a robot arm, in which a wafer is adsorbed or suctioned by a vacuum state of a vacuum nozzle when the first air valve is opened, and in which the vacuum nozzle thereof is cleaned by the N2 gas supplied thereto when the second air valve is opened.
To achieve one or more of these objects, a method of cleaning a robot arm of a wafer transfer apparatus of a CMP system includes releasing a vacuum state of the robot arm under a normal stand-by state when the robot arm does not adsorb or suction the wafer, and purging the vacuum nozzle of the robot arm with N2 gas so as to eliminate any alien substance or fumes.